A catalyst apparatus that has a catalyst having an oxidizing ability is provided in an exhaust passage of an internal combustion engine. As reducing agent is supplied to the catalyst apparatus, the temperature of the exhaust gas can be raised by the heat of oxidation generated by oxidation of the reducing agent.
For example, in the case where the catalyst apparatus is provided in the exhaust passage upstream of an exhaust gas purification apparatus composed of an NOx storage reduction catalyst (which will be hereinafter referred to as the “NOx catalyst”) and a particulate filter (which will be hereinafter referred to as the “filter”) etc, the temperature of the exhaust gas purification apparatus can be raised by supplying reducing agent to the catalyst apparatus to thereby raise the temperature of the exhaust gas as described above, when, for example, the capability of the exhaust gas purification apparatus is to be recovered.
Japanese Patent Application Laid-Open No. 2005-127257 describes a technology in which a reforming catalyst for reforming supplied fuel is provided in an exhaust passage upstream of an NOx catalyst. Japanese Patent Application Laid-Open No. 2005-127257 also discloses a technology in which the reforming catalyst is disposed at a central position of the exhaust passage so that a roundabout exhaust gas flow channel is formed around the outer circumference of the reforming catalyst.
Japanese Patent Application Laid-Open No. 2004-162611 discloses a technology in which an oxidation catalyst provided in the exhaust passage upstream of a filter is composed of a plurality of catalysts having different numbers of cells per unit area that are arranged in multiple stages from upstream to downstream.
Furthermore, Japanese Patent Application Laid-Open No. 6-106068, Japanese Patent Application Laid-Open No. 2003-120264, Japanese Patent Application Laid-Open No. 2006-161629, Publication of Japanese Translation of PCT International Application No. 9-504349 also disclose technologies pertaining to the construction or arrangement of oxidation catalyst(s) provided in the exhaust passage of an internal combustion engine.